This invention relates generally to spinnerets used to produce hollow filaments cospun with a core within the hollow portion of the hollow filament and more particularly to fabrication of spinneret capillaries used to form such filaments.
Spinneret capillaries used to form hollow filaments require complex orifices on the face of the spinneret, particularly when a hollow filament core is co-spun within another hollow filament. In one case of hollow within hollow co-spun filaments, the outer shape of each co-spun filament is formed by segments of a round configuration. These are segmented to provide points where air can enter the formed hollow portion to prevent collapsing of the filaments and to provide support to the internal sections forming the complex orifice. In another case, polymer feed cavities to the orifice are segmented to provide support as well as a point where fluid such as air can enter to support a hollow.
To obtain good filaments, it is absolutely essential that the complete orifice for each capillary be made precisely and that all orifices in a spinneret be made identical. One approach uses shaped inserts in a single hole. Another approach uses punches which are indexed into several positions. Both of these methods are tedious and time consuming and often result in orifices which lack the dimensional precision required for spinning uniform filaments. Machining a male punch is very difficult in the small complex sizes involved and still obtain precise shapes.